1. Field of the Invention
The invention relates to a process for the correction of non-rotationally-symmetrical image errors in an assembly with optical elements. The invention furthermore relates to an objective with optical elements, particularly lenses, and with a cooling device. Furthermore, the invention relates to a projection exposure device for microlithography.
2. Discussion of Relevant Art
It is known that lens heating effects lead, among other things, to non-rotationally-symmetrical temperature distributions in optical elements, particularly in lenses for semiconductor lithography objectives. Non-rotationally-symmetrical temperature distributions give rise to image errors, however, such as astigmatism in the axis and anamorphism in the distortion (.DELTA..beta.).
A static state of a non-rotationally-symmetrical temperature distribution could be corrected by suitable geometric arrangements of heat-sinking contact places, particularly on the lens periphery. However, it was found that the lens heating effects have a very marked dynamic behavior. In particular, the amplitudes of the effects are very strongly time-dependent, while the time constants are relatively long, and indeed are of the order of several minutes. For this reason, it is necessary to provide a dynamic or variably adjustable temperature distribution which can quickly and reliably oppose the non-rotationally-symmetrical temperature distributions in the optical element, in order to eliminate the said optical image errors.
Measures for the correction of rotationally asymmetric optical effects due to irradiation are already known from U.S. Pat. No. 5,805,273 European Patent EP 0 678 768. There are named for this purpose, among other things, measures for the production of rotationally symmetrical temperature distributions, for which cooling and heating devices, e.g., resistance wires and gas streams, are proposed. The production of rotationally symmetrical temperature distributions is however not an unconditional prerequisite for being able to compensate lens heating effects. The prior art device is however firstly relatively intricate and costly, and secondly, does not permit sufficient dynamics as regards changes of the temperature distribution.